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Human Brain Limits Twitter Friends to 150

The number of people we can truly be friends with is constant, regardless of social networking services like Twitter, according to a new study of the network.

May 30, 2011

Back in early 90s, the British anthropologist Robin Dunbar began studying the social groups of various kinds of primates. Before long, he noticed something odd.

Primates tend to maintain social contact with a limited number of individuals within their group. But here’s the thing: primates with bigger brains tended to have a bigger circle of friends. Dunbar reasoned that this was because the number of individuals a primate could track was limited by brain volume.

Then he did something interesting. He plotted brain size against number of contacts and extrapolated to see how many friends a human ought to be able to handle. The number turned out to be about 150.

Since then, various studies have actually measured the number of people an individual can maintain regular contact with. These all show that Dunbar was just about spot on (although there is a fair spread in the results).

What’s more, this number appears to have been constant throughout human history–from the size of neolithic villages to military units to 20th century contact books.

But in the last decade or so, social networking technology has had a profound influence on the way people connect. Twitter, for example, vastly increases the ease with which we can communicate with and follow others. It’s not uncommon for tweeters to follow and be followed by thousands of others.

So it’s easy to imagine that social networking technology finally allows humans to surpass the Dunbar number.

Not so say Bruno Goncalves and buddies at Indiana University. They studied the network of links created by 3 million Twitter users over 4 years. These tweeters sent each a whopping 380 million tweets.

But how to define friendship on Twitter. Goncalves and co say it’s not enough simply to follow or be followed by somebody for there to be a strong link.

Instead, there has to be a conversation, an exchange of tweets. And these conversation have to be regular to be a sign of a significant social bond, so occasional contacts don’t count.

Goncalves and pals used these rules to reconstruct the social network of all 3 million tweeters and studied how these networks evolve.

It turns out that when people start tweeting, their number of friends increases until they become overwhelmed. Beyond that saturation point, the conversations with less important contacts start to become less frequent and the tweeters begin to concentrate on the people they have the strongest links with.

So what is the saturation point? Or, in other words, how many people can tweeters maintain contact with before they get overwhelmed? The answer is between 100 and 200, just as Dunbar predicts.

“This finding suggests that even though modern social networks help us to log all the people with whom we meet and interact, they are unable to overcome the biological and physical constraints that limit stable social relations,” say Goncalves and co.

The bottom line is this: social networking allows us to vastly increase the number of individual we can connect with. But it does nothing to change our capability to socialise. However hard we try, we cannot maintain close links with more than about 150 buddies.

And if Dunbar is correct, that’s the way it’ll stay until somebody finds a way to increase human brain size.

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